Riser tension augmentation

ABSTRACT

A riser tension augmentation system includes a riser joint collar and a plurality of inflatable sleeves attached to the riser joint collar. Each inflatable sleeve includes a fill valve, a relief valve, and a bleed valve. A method of augmenting riser tension includes attaching a riser joint collar to a riser joint and attaching a plurality of inflatable sleeves to the riser joint collar.

BACKGROUND OF THE INVENTION

An offshore platform facilitates the drilling of a subsea wellbore through the ocean floor. After completion, the offshore platform facilitates the extraction of oil and/or natural gas from one or more reservoirs of hydrocarbons disposed below the ocean floor. Conventional offshore platforms include fixed platforms, compliant tower platforms, tension leg platforms, and floating offshore platforms such as spar platforms, drillship platforms, and semi-submersible platforms. In deep water, a floating offshore platform may be dynamically positioned or secured in place by an anchoring system. However, the anchoring system includes slack to compensate for currents, waves, and storm swells. As such, a dynamically positioned or anchored floating offshore platform may heave up and down, sway side to side, and surge front to back.

A riser string is a sectional conduit that connects the offshore platform to a subsea wellhead on the ocean floor. The riser string may be used to land a blowout preventer stack and a lower marine package on the ocean floor. During drilling operations, the riser string guides the drill string and other tools into and out of the wellbore. The riser string also serves as a return conduit through which cuttings and drilling fluids return from the wellbore to the offshore platform. The riser string typically contains drilling fluids and completion fluids used to control the pressures encountered in the wellbore. At near surface depths, the riser string itself may be prone to movement because of currents, waves, and storm swells. Thus, separately or in combination, the movement of the floating offshore platform and the riser string can result in stress fractures, buckling, and other riser string failure modes.

As the length of the riser string increases, the weight on the riser joints of the riser string increases. In addition, fluids in the riser string contribute to the weight on the riser joints. The weight on the riser joints can result in stress fractures, buckling, and other riser string failure modes. To alleviate the stress on the riser joints, the riser string is tensioned. Riser string tension provides an upward force that counteracts the weight of the riser string. Riser buoyancy modules may be used to provide tension. Riser buoyancy modules provide lift to the riser string, reduce the effective weight on the riser joints, and reduce the tension requirements of surface tensioners.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of one or more embodiments of the present invention, a riser tension augmentation system includes a riser joint collar and a plurality of inflatable sleeves attached to the riser joint collar. Each inflatable sleeve includes a fill valve, a relief valve, and a bleed valve.

According to one aspect of one or more embodiments of the present invention, a method of augmenting riser tension includes attaching a riser joint collar to a riser joint and attaching a plurality of inflatable sleeves to the riser joint collar.

Other aspects of the present invention will be apparent from the following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a portion of a conventional riser string.

FIG. 2 shows a top view of a riser tension augmentation system in accordance with one or more embodiments of the present invention.

FIG. 3 shows a side view of a portion of riser tension augmentation system in accordance with one or more embodiments of the present invention.

FIG. 4 shows a method of augmenting riser tension in accordance with one or more embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

One or more embodiments of the present invention are described in detail with reference to the accompanying figures. For consistency, like elements in the various figures are denoted by like reference numerals. In the following detailed description of the present invention, specific details are set forth in order to provide a thorough understanding of the present invention. In other instances, well-known features to one of ordinary skill in the art are not described to avoid obscuring the description of the present invention.

FIG. 1 shows a side view of a portion of a conventional riser string 100. Riser string 100 includes a plurality of sectional riser pipes 110. Riser pipes 110 are typically composed of steel or steel alloys. Each riser pipe 110 is a substantially cylindrical tube that includes an interior conduit from a first distal end to a second distal end of the pipe that allows for end-to-end flow through the pipe. Each riser pipe 110 typically has a length in a range between 20 feet and 100 feet and may vary depending on the application. Each riser pipe 110 typically has an exterior diameter in a range between 6 inches and 36 inches and may vary depending on the application. In common applications, each riser pipe 110 may be approximately 75 feet in length and may have an outer diameter of approximately 21 inches.

A riser flange 120 is attached to each end of riser pipe 110. Riser flanges 120 are typically composed of steel or steel alloys. Riser flanges 120 may be shrink-fitted to riser pipe 110 or welded in place during fabrication. Each riser flange 120 is, at its widest section, a substantially cylindrical member that includes an interior conduit and allows for mechanical attachment to riser pipe 110. Each riser flange 120 includes a riser flange joint 130 that, when mated with another riser flange joint 130, forms a riser joint 140. Riser flange joint 130 is substantially cylindrical and is typically the widest section of riser flange 120. Each riser joint 140 provides a mechanical connection between two riser pipes 110 and forms a seal such that flow may proceed through the riser pipes 110 as part of riser string 100. Typically, at least one riser joint 140 of riser string 100 is instrumented with sensors to monitor riser tension on the joint. Other designs and applications may utilize different components that serve the same function as riser flanges 120.

One or more riser pipes 110 of riser string 100 may be fitted with one or more riser buoyancy modules 150. Riser buoyancy modules 150 are typically composed of syntactic foam or other buoyant material. Each riser buoyancy module 150 typically includes two or three sectional members that are fitted together around riser pipe 110 and attached to each other by internal fasteners (not shown) or external circumferential fasteners (not shown). Each riser buoyancy module 150 is substantially cylindrical and includes an interior void for fitting riser buoyancy module 150 around riser pipe 110. One or more riser buoyancy modules 150 typically span a substantial portion of the axial length of riser pipe 110. The number of riser buoyancy modules 150 used for a given riser pipe 110 may vary depending on the length of riser pipe 110, the type of riser flanges 120 used, the type of riser buoyancy module 150 used, the desired lift to be provided, and the depth at which a particular section of riser pipe 110 will be deployed. Once constructed, riser string 100 typically includes sub-positive buoyancy such that riser string 100 does not come out of the water when disconnected from the wellhead.

Different riser buoyancy modules 150 may be used depending on the length of riser string 100, the desired lift to be provided, and the depth at which a particular section of riser pipe 110 will be deployed. Deep water riser buoyancy modules 150 are expensive and may weigh substantially more than other riser buoyancy modules 150. Each riser buoyancy module 150 typically has an exterior diameter in a range between 20 inches and 110 inches. Riser buoyancy modules 150 are typically the widest part of riser string 100. In applications where each riser pipe 110 has an exterior diameter of approximately 21 inches, each riser buoyancy module 150 may have an exterior diameter of approximately 48 inches. The exterior diameter of riser buoyancy module 150 is typically restricted by an interior diameter of the diverter housing (not shown).

The sectional members of riser string 100 are typically fabricated prior to deployment. Each riser section 160 includes riser pipe 110, two riser flanges 120 disposed on distal ends of riser pipe 110, and may include one or more riser buoyancy modules 150. Riser section 160 may be fabricated prior to transfer to an offshore platform. Alternatively, riser buoyancy modules 150 may be fitted to riser section 160 on a deck or a moon pool area of the offshore platform prior to deployment. Riser string 100 is typically constructed section-by-section on the deck or the moon pool area of the offshore platform. The construction of riser string 100 typically includes deploying one riser section 160 and then fastening another riser section 160 to it by mating two riser flange joints 130 together to form a riser joint 140. This process continues until a sufficient length of riser string 100 is constructed for the depth of the application.

Conventional offshore platforms are space constrained and weight constrained. The deck of the offshore platform may be used to store riser sections 160 prior to construction of riser string 100 as well as other required equipment. In deep water applications, the length of riser string 100 may be as much as 12,000 feet or more. As such, a large number of riser sections 160 and riser buoyancy modules 150 must be stored on the offshore platform. The deck of the offshore platform must also support the weight of other equipment, for example, the drill pipe, the rotary table, and the diverter systems. Consequently, the depth at which the offshore platform may operate may be dictated by the space and weight constraints of the offshore platform and the amount of equipment, including riser sections 160 and riser buoyancy modules 150, that may be safely deployed within a deck load capacity.

FIG. 2 shows a top view of a riser tension augmentation system 200 in accordance with one or more embodiments of the present invention. In a conventional riser string (100 of FIG. 1), riser buoyancy module 150 is attached to riser pipe 110. Additional riser buoyancy modules (not shown) may be attached to riser pipe 110 such that the riser buoyancy modules substantially span an axial length of riser pipe 110. As noted above, riser buoyancy module 150 is typically the widest part of the riser string (100 of FIG. 1). In applications where each riser pipe 110 has an exterior diameter of approximately 21 inches, riser buoyancy module 150 may have an exterior diameter of approximately 48 inches. In the top view depicted in FIG. 2, below riser buoyancy module 150, riser joint 140 is formed by a first riser flange (not shown), attached to riser pipe 110, that is coupled to a second riser flange (not shown), attached to another riser pipe (not shown), disposed below it in the riser string (100 of FIG. 1). In applications where each riser pipe 110 has an exterior diameter of approximately 21 inches, riser joint 140 may have an exterior diameter of approximately 46 inches.

In one or more embodiments of the present invention, a riser tension augmentation system 200 may be coupled to one or two riser joints 140 by one or two riser joint collars 210. Riser joint collar 210 may be a substantially circumferential member that attaches to an exterior circumference of riser joint 140. In one or more embodiments of the present invention, riser joint collar 210 may be a split or segmented shaft collar (not shown) that tightens around riser joint 140 by pin action. In one or more embodiments of the present invention, riser joint collar 210 may be a split or segmented shaft collar clamp (not shown) that tightens around riser joint 140 by clamp action. In one or more embodiments of the present invention, riser joint collar 210 may be a c-clamp (not shown) that tightens around riser joint 140 by clamp action. One of ordinary skill in the art will recognize that riser joint collar 210 may be any type of collar, clamp, fastener, or attachment mechanism suitable for securing riser joint collar 210 to riser joint 140 in accordance with one or more embodiments of the present invention.

In one or more embodiments of the present invention, a plurality of inflatable sleeves 220 may be attached to riser joint collar 210 around an exterior circumferential surface of riser joint collar 210. In one or more embodiments of the present invention, each inflatable sleeve 220 may be attached to riser joint collar 210 by one or more shackles 230 and one or more slings (not shown). Each inflatable sleeve 220 is attached to riser joint collar 210 at a bottom portion of inflatable sleeve 220 and may also be attached to another riser joint collar (not shown) disposed above it in the riser string as discussed herein with reference to FIG. 3. In one or more embodiments of the present invention, each inflatable sleeve 220 may be attached to one or more slings (not shown), the one or more slings (not shown) may be attached to one or more shackles 230, and the one or more shackles 230 may be attached to riser joint collar 210. In one or more embodiments of the present invention, each inflatable sleeve 220 may be attached to riser joint collar 210 by one or more straps (not shown). One of ordinary skill in the art will recognize that the attachment between each inflatable sleeve 220 and riser joint collar 210 may be any type of collar, clamp, fastener, or attachment mechanism suitable for securing inflatable sleeve 220 to riser joint collar 210 in accordance with one or more embodiments of the present invention.

In certain embodiments, each inflatable sleeve 220 may be a substantially cylindrical member capable of holding air or other gases. In other embodiments, each inflatable sleeve 220 may be a substantially spherical member (not shown). In one or more embodiments of the present invention, each inflatable sleeve 220 may be a doughnut shaped member (not shown) that is disposed around riser pipe 110 prior to deployment of riser pipe 110 as part of riser string (100 of FIG. 1). In certain embodiments, a plurality of doughnut shaped members (not shown) may be disposed around riser pipe 110 prior to deployment of riser pipe 110. In one or more embodiments of the present invention, instead of a plurality of inflatable sleeves 220, a single doughnut shaped member (not shown) that spans a substantial axial length of riser pipe 110 may be used. One of ordinary skill in the art will recognize that the shape of each inflatable sleeve 220 may vary in accordance with one or more embodiments of the present invention. In certain embodiments, inflatable sleeve 220 may be composed of Kevlar®. In other embodiments, inflatable sleeve 220 may be composed of a polypropylene liner with a polyester jacket. One of ordinary skill in the art will recognize that the composition of inflatable sleeve 220 may vary in accordance with one or more embodiments of the present invention. In one or more embodiments of the present invention, each inflatable sleeve 220 may comprise an inflatable air bladder (not shown) configured to hold a predetermined pounds per square inch of air or other gases. In one or more embodiments of the present invention, each inflatable sleeve 220 may comprise a protective cover (not shown) that provides mechanical and environmental protection to inflatable sleeve 220 once deployed and inflated. In one or more embodiments of the present invention, each inflatable air bladder (not shown) may be disposed within the protective cover (not shown). Each inflatable sleeve 220 may provide an adjustable amount of lift provided by the buoyancy of air or gases disposed within the sleeve 220.

In one or more embodiments of the present invention, each inflatable sleeve 220 may include one or more strap loops (not shown) disposed on an exterior surface of inflatable sleeve 220 furthest from riser string 100. In certain embodiments where more than one strap loop (not shown) is used, the strap loops (not shown) may be disposed along an axial length of inflatable sleeve 220. One or more straps 240 may be threaded through the one or more strap loops (not shown) disposed on each inflatable sleeve 220. The one or more straps 240 may include a collar (not shown), clamp (not shown), fastener (not shown), or other tightening mechanism that allows the one or more straps 240 to be tightened around an exterior circumference formed by the plurality of inflatable sleeves 220 after they are inflated. The one or more straps 240 may prevent or limit movement of the inflatable sleeves 220 from currents, waves, and storm swells after they are deployed and inflated.

In one or more embodiments of the present invention, each inflatable sleeve 220 may include one or more strap loops (not shown) disposed on an exterior surface of inflatable sleeve 220 nearest to riser string 100. In certain embodiments, where more than one strap loop (not shown) is used, the strap loops (not shown) may be disposed along an axial length of inflatable sleeve 220. One or more straps 240 may be threaded through the one or more strap loops (not shown) disposed on each inflatable sleeve 220. The one or more straps 240 may include a collar (not shown), clamp (not shown), fastener (not shown), or other tightening mechanism that allows the one or more straps 240 to be tightened around an interior circumference formed by the plurality of inflatable sleeves 220 after they are inflated. The one or more straps 240 may prevent or limit movement of the inflatable sleeves 220 from currents, waves, and storm swells after they are deployed and inflated. In one or more embodiments of the present invention, these interior strap loops (not shown) may be used to secure plurality of inflatable sleeves 220 in place prior to deployment of riser tension augmentation system 200.

In applications where riser pipe 110 is approximately 75 feet in length, each inflatable sleeve 220 may have an axial length of approximately 65 feet. In one or more embodiments of the present invention, the axial length of inflatable sleeve 220 may vary based on the length of riser pipe 110 used and the needs of a particular application. In applications where riser pipe 110 has an exterior diameter of approximately 21 inches, riser joint 140 may have an exterior diameter of approximately 46 inches and one or more riser buoyancy modules 150 may each have an exterior diameter of approximately 48 inches. In one or more embodiments of the present invention, inflatable sleeve 220 may have a diameter of approximately 21.75 inches that allow for the placement of up to ten inflatable sleeves 220 tangent to a 48-inch riser buoyancy module 150. In one or more embodiments of the present invention, the diameter of each inflatable sleeve 220 may vary based on the needs of a particular application. When inflatable sleeve 220 of riser tension augmentation system 200 is 65 feet in length and 21.75 inches in diameter, each sleeve 220 may provide approximately 10,000 pounds of lift when deployed and inflated. When ten inflatable sleeves 220 of riser tension augmentation system 200 are employed, the system 200 may provide approximately 100,000 pounds of lift. In certain embodiments, the number of inflatable sleeves 220 deployed and/or inflated may vary based on the desired lift to be provided by riser tension augmentation system 200. In certain embodiments, a plurality of riser tension augmentation systems 200 may be deployed on riser string 100.

FIG. 3 shows a side view of a portion of riser tension augmentation system 200 in accordance with one or more embodiments of the present invention. In the side view depicted in FIG. 3, to facilitate understanding, a single inflatable sleeve 220 is shown. As noted above, riser tension augmentation system 200 may include a plurality of inflatable sleeves 220 disposed around the circumference of riser joint collar 210. In addition, the side view depicted in FIG. 3 shows only a portion of a riser string. One of ordinary skill in the art will recognize that the riser string may include a plurality of riser sections 160.

Each inflatable sleeve 220 is attached to a riser joint collar 210 disposed on a bottom portion of riser section 160 depicted in FIG. 3. In one or more embodiments of the present invention, each inflatable sleeve 220 may be attached to riser joint collar 210 by one or more shackles 230 and one or more slings 350. Shackles 230 may be composed of steel or steel alloys. Slings 350 may be composed of fabric, wire, or cable. In certain embodiments, sling 350 may be adjustable. In other embodiments, sling 350 may be configured for a particular application. One of ordinary skill in the art will recognize that shackles 230 and slings 350 may vary in accordance with one or more embodiments of the present invention. Each inflatable sleeve 220 is attached to riser joint collar 210 at a bottom portion of inflatable sleeve 220. In one or more embodiments of the present invention, each inflatable sleeve 220 may be attached to one or more slings 350, the one or more slings 350 may be attached to one or more shackles 230, and the one or more shackles 230 may be attached to riser joint collar 210 disposed on the bottom portion of riser section 160 depicted in FIG. 3. In one or more embodiments of the present invention, each inflatable sleeve 220 may be attached to riser joint collar 210 by one or more straps (not shown). One of ordinary skill in the art will recognize that the attachment between each inflatable sleeve 220 and riser joint collar 210 may be any type of collar, clamp, fastener, or attachment mechanism suitable for securing inflatable sleeve 220 to riser joint collar 210 in accordance with one or more embodiments of the present invention.

In one or more embodiments of the present invention, each inflatable sleeve 220 may also be attached to another riser joint collar 210 disposed on a top portion of riser section 160 depicted in FIG. 3. In one or more embodiments of the present invention, each inflatable sleeve 220 may be attached to riser joint collar 210 by one or more shackles 230 and one or more slings 350. Each inflatable sleeve 220 may be attached to riser joint collar 210 at a top portion of inflatable sleeve 220. In one or more embodiments of the present invention, each inflatable sleeve 220 may be attached to one or more slings 350, the one or more slings 350 may be attached to one or more shackles 230, and the one or more shackles 230 may be attached to riser joint collar 210 disposed on the top portion of riser section 160 depicted in FIG. 3. In one or more embodiments of the present invention, each inflatable sleeve 220 may be attached to riser joint collar 210 by one or more straps (not shown). One of ordinary skill in the art will recognize that the attachment between each inflatable sleeve 220 and riser joint collar 210 may be any type of collar, clamp, fastener, or attachment mechanism suitable for securing inflatable sleeve 220 to riser joint collar 210 in accordance with one or more embodiments of the present invention.

In one or more embodiments of the present invention, inflatable sleeve 220 may include a fill valve 310 disposed on bottom portion of inflatable sleeve 220. In one or more embodiments of the present invention, fill valve 310 may be a pneumatic coupling that allows for inflation of inflatable sleeve 220. One of ordinary skill in the art will recognize that the size, type, location, and number of fill valves 310 may vary in accordance with one or more embodiments of the present invention.

In one or more embodiments of the present invention, inflatable sleeve 220 may include a relief valve 320 disposed on a bottom portion of inflatable sleeve 220. In one or more embodiments of the present invention, relief valve 320 may protect inflatable sleeve 220 by limiting the differential air pressure inside inflatable sleeve 220. In one or more embodiments of the present invention, relief valve 320 may provide a visual indication when inflatable sleeve 220 is filled. In one or more embodiments of the present invention, relief valve 320 may maintain a higher pressure in inflatable sleeve 220 than the sea around it to negate the effects of tidal variations on the buoyancy output of riser tension augmentation system 200. One of ordinary skill in the art will recognize that the size, type, location, and number of relief valves 320 may vary in accordance with one or more embodiments of the present invention.

In one or more embodiments of the present invention, inflatable sleeve 220 may include a bleed valve 330 disposed on a top portion of inflatable sleeve 220. In one or more embodiments of the present invention, bleed valve 330 may be a large valve that may vent air when deflating inflatable sleeve 220. When bleed valve 330 is engaged, air in inflatable sleeve 220 may be forced out of the top of inflatable sleeve 220 as the surrounding water collapses inflatable sleeve 220 from the bottom up. One of ordinary skill in the art will recognize that the size, type, location, and number of bleed valves 330 may vary in accordance with one or more embodiments of the present invention.

In one or more embodiments of the present invention, each inflatable sleeve 220 may include one or more strap loops 340 disposed on an exterior surface of inflatable sleeve 220 furthest from the riser string. In one or more embodiments of the present invention, each inflatable sleeve 220 may include one or more strap loops 340 disposed on an exterior surface of inflatable sleeve 220 nearest to the riser string. The one or more strap loops 340 facilitate circumferentially strapping together the plurality of inflatable sleeves 220 around one or more riser buoyancy modules 150. One of ordinary skill in the art will recognize that the size, type, location, and number of strap loops 340 may vary in accordance with one or more embodiments of the present invention.

FIG. 4 shows a method of augmenting riser tension in accordance with one or more embodiments of the present invention. In step 410, a first riser joint collar may be attached to a first riser joint. As noted above, the riser string is constructed section-by-section on the deck or the moon pool area of the offshore platform. The first riser joint collar may be attached to the first riser joint by a collar, a collar clamp, a c-clamp, or any other collar, clamp, fastener, or attachment mechanism suitable for securing the first riser joint collar to the first riser joint. A second riser joint collar may be attached to a second riser joint disposed above the first riser joint collar in the riser string. The second riser joint collar may be attached to the second riser joint by a collar, a collar clamp, a c-clamp, or any other collar, clamp, fastener, or attachment mechanism suitable for securing the second riser joint collar to the second riser joint.

In step 420, a plurality of inflatable sleeves may be attached to the first riser joint collar. Each inflatable sleeve may be attached to the first riser joint collar by one or more shackles and one or more slings. In certain embodiments, each inflatable sleeve may be attached to one or more slings, the one or more slings may be attached to one or more shackles, and the one or more shackles may be attached to the first riser joint collar. The plurality of inflatable sleeves may also be attached to the second riser joint collar. Each inflatable sleeve may be attached to the second riser joint collar by one or more shackles and one or more slings. In certain embodiments, each inflatable sleeve may be attached to one or more slings, the one or more slings may be attached to one or more shackles, and the one or more shackles may be attached to the second riser joint collar.

Each inflatable sleeve may optionally be configured for attachment while in a partially folded state that may unfold when inflated after deployment. While the riser sections with riser augmentation system 200 are in or near the moon pool area, the plurality of inflatable sleeves may optionally be secured by tightening straps through one or more strap loops on the exterior surface of the inflatable sleeves nearest to the riser string. The strap loops may be deployed to secure the plurality of inflatable sleeves after a control line has been inserted alongside the riser section. The straps may attach to the plurality of inflatable sleeves by one or more strap loops disposed on an exterior surface of each inflatable sleeve nearest to the riser string.

In step 430, the riser sections with riser augmentation system 200 may be deployed as part of the riser string in the water. In one or more embodiments of the present invention, riser augmentation system 200 may be deployed anywhere along a length of the riser string. In one or more embodiments of the present invention, the riser augmentation system 200 may be deployed at a depth of less than approximately 500 feet. In one or more embodiments of the present invention, the riser augmentation system 200 may be deployed at a depth of approximately 500 feet. In one or more embodiments of the present invention, the riser augmentation system 200 may be deployed at a depth in a range between approximately 500 feet and approximately 1000 feet. In one or more embodiments of the present invention, the riser augmentation system 200 may be deployed at a depth of greater than approximately 1000 feet. One of ordinary skill in the art will recognize that riser augmentation system 200 may be deployed at any depth where the inflatable sleeves may be inflated by supplied air. In step 440, one or more of the plurality of inflatable sleeves are inflated. When the riser augmentation system 200 is deployed within diving depths, a diver or a remote operated vehicle (“ROV”) may inflate one or more of the plurality of inflatable sleeves. When the riser augmentation system 200 is deployed outside of safe diving depths, the ROV may inflate one or more of the plurality of inflatable sleeves. Each inflatable sleeve may be inflated by applying air to a fill valve disposed on a bottom portion of the inflatable sleeve. The relief valve ensures that the inflatable sleeve is not over inflated and limits the differential air pressure within the inflatable sleeve. The number of inflatable sleeves that are inflated may depend on the amount of additional tension desired.

In step 450, the diver or ROV may optionally secure the inflated plurality of inflatable sleeves by tightening straps around an exterior circumference formed by the inflated plurality of inflatable sleeves. The straps may attach to the plurality of inflatable sleeves by one or more strap loops disposed on an exterior surface of each inflatable sleeve furthest from the riser string. In step 460, the diver or ROV may deflate one or more of the plurality of inflatable sleeves by opening a bleed valve disposed on a top portion of each inflatable sleeve. When the bleed valve is opened, air is forced out of the top of the inflatable sleeve as the surrounding water collapses the sleeve from the bottom-up. The inflatable sleeve may be re-inflated by closing the bleed valve and reverting to inflation step 440. Once deflated, the riser joint collar may be removed and the entire riser augmentation system may be removed from service. The same riser augmentation system may then be redeployed later. Because the deflated sleeves are foldable, the deck space required to store the riser augmentation system is minimal. The deck weight required to store the riser augmentation system is also minimal. In one or more embodiments of the present invention, a plurality of riser tension augmentation systems 200 may be deployed on the same riser string depending on the needs of the application.

Advantages of one or more embodiments of the present invention may include one or more of the following:

In one or more embodiments of the present invention, a riser augmentation system allows application of additional riser tension after a riser string is deployed.

In one or more embodiments of the present invention, a riser augmentation system allows removal of the additional riser tension before a riser string is pulled.

In one or more embodiments of the present invention, a riser augmentation system allows application of a variable amount of additional riser tension after a riser string is already deployed.

In one or more embodiments of the present invention, a riser augmentation system provides for a heavier plumb-bob effect of the riser string during reentry by eliminating the need for riser buoyancy modules on lower portions of the riser string.

In one or more embodiments of the present invention, a riser augmentation system reduces the operating load of the riser tensioning system.

In one or more embodiments of the present invention, a riser augmentation system reduces the maintenance of the riser tensioning system.

In one or more embodiments of the present invention, a riser augmentation system reduces the capital expense of offshore platform operations.

In one or more embodiments of the present invention, a riser augmentation system reduces the cross-sectional area of the riser string during reentry.

In one or more embodiments of the present invention, a riser augmentation system eliminates the need for an instrumented riser joint to monitor riser string tension.

In one or more embodiments of the present invention, a riser augmentation system reduces the number of riser buoyancy modules required for a riser string.

In one or more embodiments of the present invention, a riser augmentation system reduces the number of deep-water riser buoyancy modules needed for a riser string.

In one or more embodiments of the present invention, a riser augmentation system reduces the offshore platform deck load because fewer riser buoyancy modules are required for a riser string.

In one or more embodiments of the present invention, a riser augmentation system allows for drilling in deeper waters. Because fewer riser buoyancy modules are required, more riser may be transported for a given offshore platform deck load.

While the present invention has been described with respect to the above-noted embodiments, those skilled in the art, having the benefit of this disclosure, will recognize that other embodiments may be devised that are within the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the appended claims. 

What is claimed is:
 1. A riser tension augmentation system comprising: a riser joint collar; and a plurality of inflatable sleeves attached to the riser joint collar, wherein each inflatable sleeve comprises a fill valve, a relief valve, and a bleed valve.
 2. The system of claim 1, further comprising: a strap configured to secure the plurality of inflatable sleeves.
 3. The system of claim 1, wherein the riser joint collar comprises a shaft collar.
 4. The system of claim 1, wherein the riser joint collar comprises a shaft collar clamp.
 5. The system of claim 1, wherein the riser joint collar comprises a c-clamp.
 6. The system of claim 2, wherein each of the plurality of inflatable sleeves comprises a strap loop.
 7. The system of claim 1, wherein each of the plurality of inflatable sleeves is attached to the riser joint collar by one or more shackles and one or more slings.
 8. The system of claim 1, wherein each of the plurality of inflatable sleeves comprise an inflatable air bladder.
 9. The system of claim 8, wherein the inflatable air bladder is disposed within a protective cover.
 10. A method of augmenting riser tension comprising: attaching a riser joint collar to a riser joint; and attaching a plurality of inflatable sleeves to the riser joint collar.
 11. The method of claim 10, further comprising: deploying the plurality of inflatable sleeves attached to the riser joint collar.
 12. The method of claim 10, further comprising: securing the plurality of inflatable sleeves by a strap.
 13. The method of claim 11, further comprising: inflating one or more of the plurality of inflatable sleeves.
 14. The method of claim 13, further comprising: deflating the plurality of inflatable sleeves.
 15. The method of claim 10, wherein the riser joint collar comprises a shaft collar.
 16. The method of claim 10, wherein the riser joint collar comprises a shaft collar clamp.
 17. The method of claim 10, wherein the riser joint collar comprises a c-clamp.
 18. The method of claim 10, wherein each of the plurality of inflatable sleeves is attached to the riser joint collar by one or more shackles and one or more slings.
 19. The method of claim 10, wherein each of the plurality of inflatable sleeves comprise an inflatable air bladder.
 20. The method of claim 19, wherein the inflatable air bladder is disposed within a protective cover. 